This invention relates to a capacitive pressure sensor that senses changes in capacitance between a diaphragm and an electrode.
Capacitive pressure sensors are used in a number of applications, including climate control systems and semiconductor processing. A pressure sensor has a housing, an input in the housing for receiving a fluid (gas or liquid) whose pressure is being sensed, a conductive flexible diaphragm and an electrode next to the diaphragm. The diaphragm and electrode have a capacitance between them. The sensor senses changes in the capacitance as the diaphragm moves relative to the electrode in response to pressure from the fluid.
It can be desirable to have a baffle between the inlet for the fluid whose pressure is being sensed, and the flexible diaphragm. The baffle helps prevent contaminants from contaminating the diaphragm. U.S. Pat. No. 5,811,685, which is hereby incorporated by reference for all purposes, describes a baffle and also some previous baffle designs. The patent further discusses reasons for and benefits of a baffle in such a sensor.
A capacitive pressure sensor of the present invention has a housing with an inlet for receiving a fluid, a diaphragm that flexes in response to pressure in the fluid, and a baffle designed to provide a high aspect ratio radial path for the gas molecules to flow between the inlet and the diaphragm. Preferably, the invention also includes a particle trap system (which is also a baffle), positioned such that the baffle is between the trap system and the diaphragm. The aspect ratio (the ratio of the radial length to the gap) of a path formed by the baffle is greater than 10, and preferably greater than 50.
In another aspect, the capacitive pressure sensor has a housing with an inlet for receiving a fluid, a diaphragm that flexes in response to pressure in the fluid, and a baffle between the inlet and the diaphragm, with the baffle designed so that a path taken by molecules from the inlet to the diaphragm creates molecular flow, as opposed to laminar flow.
The baffle is preferably positioned close to the diaphragm so that there is a small volume between them, so that the sensor responds quickly to changes in gas pressure.
The higher aspect ratio path formed by the baffle increases the likelihood that molecules will stick to a surface of the baffle or the housing before reaching the flexing portion of the diaphragm, thereby protecting the diaphragm from deposition. The small volume between the baffle and diaphragm does not reduce response time, as a large volume would. Other features and advantages will become apparent from the following detailed description, drawings, and claims.